Supporting (fixturing) and manufacturing of workpieces with complex geometry are frequent in the manufacturing of parts of aircrafts and automobiles. The workpieces to support and fixture can be very flexible and thin. Typical manufacturing operations to execute are drilling, holing, opening of windows, welding. Generally, especially for aircrafts, the workpieces are large and consequently very deformable, therefore the supporting (fixturing) device must be able to preserve the geometry of the workpiece preventing deformations caused by uneven distributions of the support. Such deformations would result in rejection of the workpiece.
The supporting (fixturing) devices commonly in use have a surface in contact with the workpiece fixed or in part adaptable to the geometry of the workpiece. Reconfigurable supporting (fixturing) devices have been proposed comprising actively or passively movable supports which can be moved to conform to the workpiece geometry and can then be blocked, freezing the shape.
Such adjust-and-freeze supporting devices work satisfactorily with workpiece geometries in a limited range. They are not technically efficient with workpieces with significantly different shapes while they are particularly convenient for repeated operations on a limited set of geometries. Also from an economic point of view, these adjust-and-freeze supporting devices are convenient in the case of repeated manufacturing operations on workpieces with similar geometries since the cost of one supporting device is spread over several workpieces.
An example for the support of thin bodies can be found in EP1245317.
Adaptable supporting (fixturing) devices have been proposed that consist of a matrix of support points or areas, each one mounted on a device able to move those supporting points with a mobility depending on the complexity of the geometry of the workpiece to support.
The configuration of the geometry of the support may be either manual or automatic and is always performed before the positioning of the workpiece.
An example of this type of devices is in EP1728594. It comprises matrices of posts rigidly connected to a common base frame. The posts have variable lengths with elements of interfacing to the supported workpiece at the free extremity.
Alternatively, it is possible to use systems comprising mobile elements of support connected to a common base frame or with extensible or articulated support units as described in WO2007010355 and U.S. Pat. No. 5,732,194.
Furthermore, support systems have been proposed, as in JP9061103, comprising independent support units that can be positioned and fixed to a common frame and so adapted to the surface of the body to support.
The supporting devices with an entirely adjustable surface have the disadvantage to be complex and with high cost, especially if used for large bodies requiring a high density of support points to prevent deformation.
Finally, the supporting devices with independent support units have the disadvantage that the manufacturing process must be interrupted for adjustment and moreover the adjustment requires in the majority of the devices significant operations (often manual). An external measuring system is required (e.g. laser) for the fine-tuning of the positions of the supports, further increasing the time and labor required at any reconfiguration.
Continuous adaptable/reshapable envelopes, with dimensions comparable to the ones of the body to support, have been proposed as an alternative to the systems composed of independent support units. They are filled with material (e.g. magnetorheologic) whose physical state can be commanded and changed between deformable (e.g. fluid or plastic) and stiff, so that the envelope can take and keep shapes that are also significantly different.
This solution presents problems if applied to the support of workpieces subject to mechanical manufacturing and machining since typical machining operations like drilling, welding, milling may damage the envelope.
Moreover, since machining requires in general a high density of supports (to provide proper and stiff fixturing), large bodies have to be manufactured in different phases (subregion by subregion): the manufacturing operations are carried out in a region and the support (fixturing) can be conveniently concentrated in that region where stiffness and load capacity are required.
Inevitably, machining operations produce swarf which deposits on the common base frame over which the support units move. This complicates or makes impossible the motion and repositioning of the support units without manual cleaning of the base frame and consequent interruption of the manufacturing operations.
An unsatisfied practical need exists of a device for the support of workpieces with complex geometry, said device being able to provide automatically a continuous support preventing the deformation of the workpiece in the region subject to machining, using for this purpose simple and cost-effective solutions, overcoming the need for manual intervention during the progression of the manufacturing operations.